The enzyme from Leishmania (both amastigote and promastigote forms) catalyses the reduction by NADPH of folate and a wide variety of unconjugated pterins, including biopterin, to their tetrahydro forms. It also catalyses the reduction of 7,8-dihydropterins and 7,8-dihydrofolate to their tetrahydro forms. In contrast to EC 1.5.1.3 (dihydrofolate reductase) and EC 1.5.1.34 (6,7-dihydropteridine reductase), pteridine reductase will not catalyse the reduction of the quinonoid form of dihydrobiopterin. The enzyme is specific for NADPH; no activity has been detected with NADH. It also differs from EC 1.5.1.3 (dihydrofolate reductase) in being specific for the Si-face of NADPH.